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First GMC *never* used Olds or Buick engines in their trucks. The Buick rumour probably started because someone saw a listing in a parts catalog or somewhere concerning a 401 "GMC" engine and assumed that it since it was a"401, that it must be a similar displacement Buick 401 V8. Not so. A 401 GMC engine was just that - a "401 GMC" - and a V6 to boot!

Here's the real deal on the somewhat confusing GMC engine line from '55 through the mid 60's.

U.S built GMC's did use a version of the Pontiac V8 from '55 through '59. In 55 they used a 287 Pontiac, in '56- a 316, and '57- a 347. In '58 and '59 they used a 336 V8 that was a small bore (3 7/8) vesion of the Pontiac 370 V8. To muddy the waters a bit more, the GMC advertising guys gave the Pontiac engines one extra cube in the brochures in '55 and and '56. Hence the the "Pontiac" 287 was advertised as the "GMC 288" and the Pontiac 316 became the "GMC 317" engine. In these years too, if a 6 cylinder engine was used, the base engine was the 235 inline Chevy. A 261 6 banger that was a stroked Chevy 235 was also offered. In the U.S., GMC dropped the Pontiac engines after '59 and came out will their own, all new 60 degree V6 engine for 1960 - starting with a 305 V6. This engine was expanded over the years and depending on the model and gvw rating, became available in 305, 351, 401 and 478 inch sizes-all of them V6's! They even produced a massive 702 "twin six" V12 version for use in the GMC 'big trucks'.

Canadian built 6 cylinder '55 through '61 GMC's used the 235 and 261 versions of the Chevy 6. '55-59 Canadian built V8 GMC's never used the Pontiac engines. Instead, they came with 265 small block Chev V8's in '55, 56 and '57 (and into early '58) with the 283 Chev V8 becoming optional in '57 and the standard V8 in mid '58 through '67. In '62 the 327 and (1962-'65) 348-409 Chevy engines became extra cost options in various model Canadian GMC's. Beginning in '66, 396 and 366-427 Chevy big blocks were used as optional engines after the phase out of the 348-409 Chevies. Canadian built light duty trucks (under 10,000 GVW) never used the big U.S built V6's- they were simply rebadged Chevies and used the standard Chevy inline 6 or 283-327 small block (or 348-409 or 366-427 V8's in the heavy trucks), although the 401, 478 V6 and 702 V12 could be "special ordered "in the big (over 10,000 lb GVW) GMC trucks in Canada.

Hope this helps clear up some mysteries.

mart

Sorry you are wrong. Olds engine was used in the bigger GMC. 2 1/2 TON trucks. The buick engine was used in the chevy big trucks The chevy 235 and 261 was never used in the US GMC trucks. They used there own 6 cyl. If you would like to see these come and see me. I can show you them, I have them all.

11-14-2009 07:53 AM

Gear~head

What an interesting read. thanks for sharing

10-30-2009 04:46 PM

Y2K

Interesting thread,did a Google search on '57 GMC V8 and wound up here.

My Dad had a '57 Panel in the late '60's with a Pontiac V8 and Hydramatic trans,wish I had it today.

03-14-2009 01:53 PM

GiantMountainClimber

I am quite familiar with the Buick/ Chev truck engine and they were offered in the larger Chev trucks, not only school buses. The Olds/GMC 371/370 was a very similar situation. The 370 GMC was the 1957 Olds version beefed up for truck use. Olds went on and changed the position of the main thrust bearing. I rediscovered this just last week when I was looking for a set of mains for a 370 GMC and 57 Only Olds mains are the same. Olds went on to the 394 which was 4.125 bore instead of the 4.0 of the 371. The 370 as well as inline 6 GMC line was dropped in 1960 for the V6. However the 270 inline 6 was produced through 62 for package delivery trucks. My theory is that they did not have time to redesign the dog house in the package delivery trucks to accommodate the wider V blocks.

03-14-2009 01:49 PM

Trucknut

Having grown up in Pontiac, Michigan in the 50's, I can tell you that Pontiac Motor plant was about two miles away from the GMC truck plant that built Chevy and GMC trucks. That could be a clue in regard to the 347 ending up in the GMC trucks. The 347 was also available in the Pontiac with tri-power.

03-14-2009 10:29 AM

MARTINSR

I don't know about GMC but as that Chevrolet bus chassis proves, they most certainly did use the Buick 322 from 55-59. My brother is a Buick Nailhead specialist and found this to be true while searching out parts for Buicks. The odd thing is, they revamped the motor quite a bit. He has matched up the part numbers between the "Chevy/Buick" 322 and the Buick 322 and found that there are MANY parts that don't have the same numbers and were "revamped" by Chevy. Most notably the Chevy/Buick has a twin roller timing chain! What is odd is that Buick had dropped the 322 in 56 but Chevy used it up until 59.

Brian

03-14-2009 06:18 AM

1ownerT

A lot of interesting info.
I had a 63 GMC pickup, 305 V6, kick myself in the butt to this day for selling it.

03-13-2009 10:01 PM

GiantMountainClimber

I found this site while searching for a set of pistons for a 1957 GMC 370 engine. Just for the record, GMC did use an Oldsmobile engine in their 550 and 600 series trucks from 57-59. It was a 371 Oldsmobile block, but GMC called it a 370. I know this for a fact because I drove one several hundred thousand miles almost 50 years ago and rebuilt the engine several times. The 55 -59 GMC parts book for the 550 series through 970 series lists the engine and many parts carry the same part number as Olds 371. The major differences were the 370 GMC used a forged dished piston, positive rotating valves and an adapter which allowed using a truck Holly "teapot" carb on top of an Olds manifold. I also invite anyone interested in old GMC's to visit the OldGMCforums which is hosted by Oldcarkook.

10-27-2008 10:32 AM

inthenorth

Pontiac Engins In A Gmc

WELL GUYS GO TO www.antiquechevytrucks.com thay talk about how gmc put the poniac motor in the gmc and gmc put a gmc tag on it and through the years gmc had to follow pontiacs choices on changes to the motors gmc put in there trucks.
i cant rember what categorie its in but youll find it. i hope this bit of info helps clear things up

03-28-2004 01:06 PM

oldcarkook

Clearing the air on GMC engines

Ladies and Germs: It has come to my attention that some facts about GMC truck engines may in dispute here and I have stopped by to clear the air and set forth factual information, backed up by original factory documentation to any non-believers.

A list of corresponding applications (models) for these engines may be found on my website under "Serial Numbers" 1955 to 1959.

I have no documentation to state the origins of these motors such as whether they were adopted Pontiac, Buick, or other GM engines, but I do have the original factory lists of parts for each of these engines in their respective applications.

Since you're on the subject of oddball engines, why is no one discussing the GMC 702 V12 here? Ah HA! Now there's a very different motor for sure. There were also 305, 351, and 401 GMC V6 engines, and you can deduce that the 702 was a "fused pair" of 351's. Jolly Goodfellow's 6066 GMC site talks extensively about the rare 702 and he has at least two of those engines as I recall. If all this is a bit overwhelming to digest, try evaluating the GMC straight six cylinder engines from 1939 to 1959 for a real eye opener in numbers, configurations, and engine sizes!

Additionally, I have some Chevy data which I don't generally admit to since I am really a died in the wool GMC man, but...

In that Chevy data, I find the 1958 Chevrolet "322 cubic inch Loadmaster V8" engine used in schoolbus chassis number 10802 ONLY, a 54-60 pupil chassis.

While these engines are certainly obscure, they absolpositutely did exist and they absolpositutely were put into the applications indicated above.

In fact, since I don't publish Chevy stuff on my GMC site, here's the Chevy proof for any non-believers:

For the other listing, you'll need to poke around my site some.

Never start a pissin' contest with a skunk.

03-28-2004 12:23 PM

Nightfire

Everyone said it already but I'll hqve to say it too......thanks a lot for giving us this little bit of history and that I could learn something new today.

I wish I could know more qbout hot rodding history and stuff instead of just the cars, years, models and looks. Some ppl on this site have just amazed me. They know exactly what year, model and even engine is of a car just by looking at a 15+ digit serial number. I always wish I could know more about hot rodding heritage.

Mike

03-28-2004 12:13 PM

mr55chev

Well, boy oh boy, did I get leveled! Never is a powerful word, and certainly positive.
The first problem is your statement about the 261 engine. In the US, it came out in 1954, and was an overbored 235. The bore went from 3.5625 to 3.75. It is good to know that in Canada they increased the crankshaft stroke, as you said it is a "stroked 235". Wonder why they did that? You would think they would save the money and use the version they developed for the USA.
Next, the never part. As a college student in the late '50's, I was the product placement director (lot boy) at the Chevrolet dealer in my home town. I cleaned up and prepped out medium duty units with 322 inch Buick vertical valve V8's in them, from the factory. Later, in 1970, I bought my 55-2 GMC from a farmer in Rigby, Idaho with a frozen up stroked 235 in it (funny, I always thought it was a 248/270, never did check cause it was RUINED
by pure water being left in it over a -30 degree Idaho winter). I swapped in an early (303 CID) Olds V8 I had available, and took the result past the GMC dealership who had pointed out the farmyard where the truck was sitting. He looked at the Olds under the hood, and said, you know, GMC put those engines in their trucks back then - and led me to the trade in lot where there was a mid-fifties GMC 2-1/2 ton spud hauler truck with a by-gosh genuine 370 cubic inch GMC V8 engine with valve cover bolts thru the rocker covers centers - sure looked like an Olds to me, and I guess the late Bill Treasure should know - he was the largest GMC dealer in the Intermountain West.
When I went to document this data, I could not find much on the internet. I found a reference to one in an engine color site, and another in the Egge piston site. So, I went to Rob English, whose site is OldGMCTrucks.com and he spent some time in his huge collection of data books and came up with documentation that they WERE used - and stated, that through all his years of studying GMC,s they were new to him, and that you learn something new every day.
From what I know, your data about the 60 up V6's is accurate, and your data about the Pontiac V8 in the 55-59's is also accurate. Canadian vehicles were handled differently, and I can well recall a visitor in the repair lanes of the Ogden, Utah Chevrolet dealership in, I believe, late 1959 with what looked exactly like a '60 Pontiac, except the wheels were way inside the fenders (unlike the "wide track Pontiac's of the USA) and the hood was open and the familiar Chevrolet 235/261 6 cyl was under it - a real eye-opener. I think it was an Acatian, or some such name, had Manitoba license plates.

First GMC *never* used Olds or Buick engines in their trucks. The Buick rumour probably started because someone saw a listing in a parts catalog or somewhere concerning a 401 "GMC" engine and assumed that it since it was a"401, that it must be a similar displacement Buick 401 V8. Not so. A 401 GMC engine was just that - a "401 GMC" - and a V6 to boot!

Here's the real deal on the somewhat confusing GMC engine line from '55 through the mid 60's.

U.S built GMC's did use a version of the Pontiac V8 from '55 through '59. In 55 they used a 287 Pontiac, in '56- a 316, and '57- a 347. In '58 and '59 they used a 336 V8 that was a small bore (3 7/8) vesion of the Pontiac 370 V8. To muddy the waters a bit more, the GMC advertising guys gave the Pontiac engines one extra cube in the brochures in '55 and and '56. Hence the the "Pontiac" 287 was advertised as the "GMC 288" and the Pontiac 316 became the "GMC 317" engine. In these years too, if a 6 cylinder engine was used, the base engine was the 235 inline Chevy. A 261 6 banger that was a stroked Chevy 235 was also offered. In the U.S., GMC dropped the Pontiac engines after '59 and came out will their own, all new 60 degree V6 engine for 1960 - starting with a 305 V6. This engine was expanded over the years and depending on the model and gvw rating, became available in 305, 351, 401 and 478 inch sizes-all of them V6's! They even produced a massive 702 "twin six" V12 version for use in the GMC 'big trucks'.

Canadian built 6 cylinder '55 through '61 GMC's used the 235 and 261 versions of the Chevy 6. '55-59 Canadian built V8 GMC's never used the Pontiac engines. Instead, they came with 265 small block Chev V8's in '55, 56 and '57 (and into early '58) with the 283 Chev V8 becoming optional in '57 and the standard V8 in mid '58 through '67. In '62 the 327 and (1962-'65) 348-409 Chevy engines became extra cost options in various model Canadian GMC's. Beginning in '66, 396 and 366-427 Chevy big blocks were used as optional engines after the phase out of the 348-409 Chevies. Canadian built light duty trucks (under 10,000 GVW) never used the big U.S built V6's- they were simply rebadged Chevies and used the standard Chevy inline 6 or 283-327 small block (or 348-409 or 366-427 V8's in the heavy trucks), although the 401, 478 V6 and 702 V12 could be "special ordered "in the big (over 10,000 lb GVW) GMC trucks in Canada.

Hope this helps clear up some mysteries.

mart

10-16-2003 08:06 PM

kitkar

That was really interesting, guys. I'm glad I read this thread.

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